Estimation of potential evapotranspiration from extraterrestrial radiation, air temperature and humidity to assess future climate change effects on the vegetation of the Northern Great Plains, USA PublicDeposited

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Descriptions

The potential evapotranspiration (PET) that would occur with unlimited plant access to water is a central
driver of simulated plant growth in many ecological models. PET is influenced by solar and longwave
radiation, temperature, wind speed, and humidity, but it is often modeled as a function of temperature
alone. This approach can cause biases in projections of future climate impacts in part because it
confounds the effects of warming due to increased greenhouse gases with that which would be caused by
increased radiation from the sun. We developed an algorithm for linking PET to extraterrestrial solar
radiation (incoming top-of atmosphere solar radiation), as well as temperature and atmospheric water
vapor pressure, and incorporated this algorithm into the dynamic global vegetation model MC1. We
tested the new algorithm for the Northern Great Plains, USA, whose remaining grasslands are threatened
by continuing woody encroachment. Both the new and the standard temperature-dependent
MC1 algorithm adequately simulated current PET, as compared to the more rigorous PenPan model
of Rotstayn et al. (2006). However, compared to the standard algorithm, the new algorithm projected a
much more gradual increase in PET over the 21st century for three contrasting future climates. This
difference led to lower simulated drought effects and hence greater woody encroachment with the new
algorithm, illustrating the importance of more rigorous calculations of PET in ecological models dealing
with climate change.